1. Field of the Invention
The present invention relates to a magnetic body using non-magnetic semiconductor.
2. Description of the Background Art
Conventionally known magnetic materials for forming magnetic bodies include natural magnets such as magnetite (Fe3O4), alloy steel magnets such as chrome steel and high cobalt steel, and magnets containing alnico, ferrite, or rare earth elements.
Conventionally, circuits such as magnetic memory media and magnetic sensors have been manufactured using these magnetic materials. However, it has been necessary to manufacture these circuits separately from electronic parts on LSI substrate such as transistors because of the various problems related to the manufacturing process including the fact that these magnetic materials all contain metals which have poor affinity with materials such as silicon and GaAs used for LSI substrate, and this has been an obstacle for realization of compact and densely integrated electronic circuits.
On the other hand, there has been theoretical propositions to manufacture magnetic bodies using a flat-band structure. Here, the flat-band structure refers to a band structure in which energy dispersion of electrons has hardly any wave number dependency.
In general, in the case of filling electrons into degenerate energy levels, there arises an effect to align spins parallel as much as possible in order to gain the exchange energy. A typical example of this effect is the so called Hund""s first law in the atomic nucleus model.
The fact that the effect to align spins parallel as much as possible arises in the case of filling electrons into a dispersionless (i.e., strongly degenerate) system such as the flat-band structure has been predicted by Lieb, Mielke, and Tasaki by using a mathematical model assuming the short distance Coulomb interaction such as Hubbard model. (See: E. Lieb, xe2x80x9cTwo Theorems on the Hubbard Modelxe2x80x9d, Physical Review Letters, Vol. 62, No. 10, pp. 1201-1204, March 1989; A. Mielke, xe2x80x9cFerromagnetism in the Hubbard model on line graphs and further considerationsxe2x80x9d, J. Phys. A: Match. Gen. 24, pp3311-3321, 1991; and H. Tasaki, xe2x80x9cFerromagnetism in the Hubbard Models with Degenerate Single-Electron Ground Statesxe2x80x9d, Physical Review Letters, Vol. 69, No. 10, pp. 1608-1611, September 1992.)
However, their propositions are based on many approximations such as the assumption of the short distance Coulomb interaction that are used in solving the mathematical model, and whether the flat-band ferromagnetic states predicted by using such mathematical models can be actually realized or not cannot be judged correctly without carrying out accurate calculations in accordance with the real materials.
Based on these propositions of Lieb, Mielke and Tasaki, there have been theoretical propositions to manufacture magnetic bodies using non-metal material such as Graphite, Ga atoms and As atoms. (See: N. Shima, et al., xe2x80x9cElectronic Structure of Superhoneycomb Systems: A Peculiar Realization of Semimetal/Semiconductor Classes and Ferromagnetism, Physical Review Letters, Vol. 71, No. 26, pp.4389-4392, December 1993; and R. Arita, et al., xe2x80x9cFerromagnetism in a Hubbard model for an atomic quantum wire: A realization of flat-band magnetism from even-membered ringsxe2x80x9d, Physical Review B, Vo. 57, No. 12, pp. R6854-6857, March 1998, for example.)
However, it has been practically difficult to artificially synthesize materials that realize the flat-band or arrange small atoms exactly as designed, so that it has been impossible to manufacture the flat-band magnetic bodies in practice.
Thus the conventional magnetic bodies made of metal elements have no affinity with the semiconductor LSI process, so that it has been impossible to manufacture them on the same substrate.
It has also been impossible to form a material having a flat-band structure that exhibits ferromagnetism by using non-magnetic materials, due to difficulties in synthesizing or manufacturing such a material.
Also, some conventional magnetic bodies contain harmful materials such as manganese and chromium, and there are great concern about their adverse effects on human bodies and environment, and they are also a factor for increasing the recycle cost.
It is therefore an object of the present invention to provide a practically realizable semiconductor magnetic body having a flat-band structure, by forming quantum dot array using the semiconductor manufacturing and growth techniques.
According to one aspect of the present invention there is provided a semiconductor magnetic body, comprising: semiconductor quantum dots arranged on lattice points such that electrons can transfer between neighboring quantum dots and the electron energy band contains a flat-band structure, where each quantum dot is a structure in which electrons are confined inside a region which is surrounded by high energy potential regions, and the flat-band structure is a band structure in which energy dispersion of electrons has hardly any wave number dependency.
Other features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings.